I’m fed-up with google Sketchup. It took me hours to get this far:
After a lot of wasted time and effort struggling with its awful interface I got something tending towards what I wanted:
But it turned out to be unprintable because sketchup may be good with surfaces but simply doesn’t care about solids. So I’m switching to FreeCAD now.
FreeCAD has a learning curve… but at least the result is a printable solid:
With some help from Extrudy:
Extrudy has the drawback that it makes big solid shapes and doesn’t really support creating a hollow shell, but most 3D printing sites offer tools to automatically “hollow out” those, and if you make the escape hole large enough it amounts top the same thing.